Natural wax-assisted anisotropic crystallization on hierarchical polydimethylsiloxane sponge: Harnessing interfacial...

Oil spills and oily wastewater pose significant environmental threats and technological challenges due to the persistence, dispersion, and toxicity of hydrocarbon pollutants, especially in stable nanoemulsion forms. Nanosorbents have emerged as promising solutions, yet there remains a critical need to explore materials with high oil selectivity, mechanical durability, and sustainable design. This study introduces a sustainable material synthesized by incorporating plant-derived microcrystalline Carnauba wax and vertically aligned nanocrystalline Tropaeolum majus (T. majus) wax within a polydimethylsiloxane (PDMS) matrix. This integration, achieved through eco-friendly sugar- and water-in-oil emulsion templating, wax blending, and in-situ recrystallization, yields a hierarchical, ultra-porous (91 %) sponge that is lightweight, mechanically robust (compressive strength up to 10 kN), and capable of stable, non-leaching oil retention for efficient separation of oil-water mixtures and nanoemulsions. The vertical orientation of wax nanocrystallites significantly lowers interfacial surface energy, enhancing preferential oil sorption, as validated by contact angle analysis and sorption kinetics across various oil-water configurations. This interfacial modulation enables high oil uptake (27 g·g^-1; 4-fold enhancement) and separation efficiency (96 % for microemulsions and 68 % for nanoemulsions) under both batch (1.5 L·h^-1) and continuous flow (6250 L·m^-2·h^-1) conditions, while maintaining mechanical durability and recyclability over 115 reuse cycles. Moreover, the sponge exhibits robust performance across a wide temperature and pH range, achieving 82 % oil removal and a 10-fold reduction in chemical oxygen demand (COD) during refinery wastewater treatment. By revealing how natural wax-induced crystallization modulates interfacial energy, this study advances understanding of structure-function relationships and supports sustainable separation technologies in colloid and interface science.